V-ribbed belts having a large number of pores on their pulley contact surfaces are known.
For example, Patent Document 1 describes a V-ribbed belt in which a portion including a pulley contact surface is at least partially made of a porous rubber composition having an air content of 5-20%.
Patent Document 2 describes a V-ribbed belt having a two-layer structure including an outer adhesion rubber layer and an inner compression rubber layer. In this V-ribbed belt, hollow particles are blended into a rubber composition forming the compression rubber layer, and part of the hollow particles exposed at the pulley contact surface is partially cut away to form a large number of cellular pores.